The present invention relates to a vehicle sensor system, and more particularly to a communication system that operates through a rotary interface within a wheel hub assembly.
Vehicles often include a sensor system, which measures the pressure of each tire and provides continuous monitoring of the pressure to a driver of the vehicle. Recently, these systems may become mandatory in the industry.
Such a system generally includes a controller mounted within the vehicle and remote circuitry located in each tire for detecting the tire pressure and transmitting the detected tire pressure to the controller. The controller receives the detected tire pressure and presents it to the driver.
As will be appreciated, providing power for, and communicating with, the remote circuitry in each tire of the vehicle may be relatively difficult. Typically, the systems are limited to certain frequency bands and to specific power levels. National and international regulations that govern these devices require testing and certification to a certain standard. Given that the standard is low in RF output power, the system may have difficulty in meeting certain functional requirements. To meet certain requirements, each specific application is measured and tuned to multiple parameters. One difficult parameter is the difference in the quantity of steel in the tire and tire-to-tire variation. Another difficult parameter is the position and rotation of the tire/wheel speed in normal driving situations in which the RF carrier may be unintentionally modulated.
Another difficulty is the necessity to provide significant battery life to ensure the electronics will operate without replacement. Conventional systems often utilize coin cell batteries that expire or wear down from extended use and temperature.
Yet another difficulty is that the system must be robust. The current systems are often integrated into the valve stem assembly. Upon a tire change, care must be taken not to damage the seal or electronics. Due to the exposed valve stem position, conventional systems may receive external shock that could permanently damage or destroy functionality. In addition, care must be taken with balancing the tire as the stem mounted sensor has mass which must be offset.
Accordingly, it is desirable to provide an inexpensive and robust communication system for a tire mounted sensor system which operates through the rotational interface with minimal interference.